This invention relates to control apparatus of direct current motors, and more particularly to control apparatus utilizing semiconductor switches such as power transistors or thyristors.
According to one prior art DC motor control apparatus, a DC motor is connected to a source of direct current through a semiconductor switch, as shown in FIG. 1 and the speed of the motor is controlled by means of a control device which relatively controls the ON period and OFF period of the semiconductor switch thereby to control the motor armature voltage. However, with such connection large power is consumed by the semiconductor switch so that it is necessary to use transistors of relatively large size.